Thrust bearing assembly

ABSTRACT

A thrust bearing assembly generally includes a cage and a plurality of rolling elements. The cage has first and second cage halves with each cage half having a respective radial segment with a plurality of circumferentially spaced openings. Each opening has an opening perimeter. The cage halves are interconnected with portions of the radial segments circumferentially between the plurality of openings abutting along a given plane and the respective openings aligned to defined rolling element pockets. The rolling elements are positioned in the rolling element pockets such that a centerline of each rolling element lies in or in proximity to the given plane. A flange extends along at least a portion of each opening perimeter to retain the rolling elements within a respective one of the rolling element pockets.

CROSS REFERENCE TO OTHER APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/816,803, filed Aug. 21, 2007, which is a 371 application ofPCT/US2006/005789, filed Feb. 17, 2006, which claims priority to U.S.Provisional Patent Application No. 60/654,916, filed on Feb. 22, 2005,the entire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a thrust bearing assembly and inparticular to a needle roller thrust bearing assembly.

BACKGROUND OF THE INVENTION

Referring to FIGS. 11 and 12, an example of a prior art needle rollerthrust bearing 1 is shown. The bearing 1 includes a plurality ofcylindrical rolling elements 2 arranged radially from a center ofrotation. The rolling elements 2 are retained and guided by a bearingcage 3, which forms the primary structure of the bearing 1.

There are several types of construction currently used to producemetallic needle roller bearing cages 3. FIGS. 13 and 14 show a thrustbearing 1A with a cage 3A that is constructed of two halves 4. Each half4 has rectangular window openings 5 which are slightly smaller in widththan the diameter of the rolling elements 2. Each cage half 4 also hascircumferential flanges 6 which are directed inwardly towards theopposite member. When joined together, these two cage halves 4 form abox which provides structural integrity for the assembly, along withguidance for the rolling elements 2 and their retention in bothdirections.

A prior art thrust bearing 1B with a cage 3B having another constructionis shown in FIGS. 15 and 16. In this construction, the cage 3B is formedfrom a single piece of metal into a shape which, along with speciallyshaped openings, retains and guides the rolling elements 2. Incross-section, this type of cage 3B has a shape similar to that of theGreek letter sigma (Σ).

Another thrust bearing 1C having a cage 3C of yet another constructionis shown in FIGS. 17 and 18. Here, the cage 3C has a material thicknessclose to the diameter of the rolling elements 2 and has rectangularopenings 5 to accept the rolling elements 2. Retention is provided bystaking 7 or otherwise forming the cage face near the openings 5 so thatthese are made smaller than the diameter of the rolling element 2.

SUMMARY OF THE INVENTION

In one embodiment, a thrust bearing assembly includes a cage and aplurality of rolling elements. The cage has first and second cage halveswith each cage half having a respective radial segment with a pluralityof circumferentially spaced openings. Each opening has an openingperimeter. The cage halves are interconnected with portions of theradial segments circumferentially between the plurality of openingsabutting along a given plane and the respective openings aligned todefine rolling element pockets. The rolling elements are positioned inthe rolling element pockets such that a centerline of each rollingelement lies in or in proximity to the given plane. A flange extendsalong at least a portion of each opening perimeter to retain the rollingelements within a respective one of the rolling element pockets. Theflange may include a smooth rolled surface adjacent to each rollingelement.

In another embodiment, a thrust bearing assembly includes a cage and aplurality of rolling elements. The cage has first and second cage halveswith each cage half having a respective radial segment with a pluralityof openings. Each opening has an opening perimeter and the cage halvesare interconnected with portions of the radial segments abutting along agiven plane. The respective openings are aligned to define rollingelement pockets. The rolling elements are positioned in the rollingelement pockets such that a centerline of each rolling element lies inor in proximity to the given plane. A flange extends along the entireperimeter of each respective opening to guide and retain the rollingelements within a respective one of the rolling element pockets.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial isometric view of a needle roller thrust bearingassembly that is a first embodiment of the present invention;

FIG. 2 is a cross-sectional view along the line 2-2 in FIG. 1;

FIG. 3 is a cross-sectional view similar to FIG. 2 showing anotherembodiment of a thrust bearing assembly;

FIG. 4 is an exploded view of a portion of the cage as indicated by thecircle 4 in FIG. 1 with the rolling elements removed for clarity;

FIG. 5 is a cross-sectional view along the lines 5-5 in FIG. 1;

FIGS. 6-8 are cross-sectional views similar to FIG. 5 illustrating otherembodiments of a thrust bearing assembly;

FIG. 9 is a cross-sectional view illustrating the needle roller thrustbearing assembly of FIG. 1 positioned between a pair of bearingsurfaces;

FIG. 10 is a cross-sectional view similar to FIG. 9 showing anotherembodiment of a thrust bearing assembly;

FIG. 11 is a cross-sectional view along line 11-11 in FIG. 12;

FIG. 12 is a front elevation view of a prior art thrust bearing;

FIG. 13 is a partial cross-sectional view of an alternative prior artthrust bearing;

FIG. 14 is a partial isometric view of the cage of the thrust bearing ofFIG. 13;

FIG. 15 is an isometric view of a cage of another prior art thrustbearing;

FIG. 16 is a partial cross-sectional view of the alternative thrustbearing using the cage of FIG. 15;

FIG. 17 is an isometric view of yet another alternative prior art thrustbearing;

FIG. 18 is a cross-sectional view along the line 18-18 in FIG. 17;

FIG. 19 is a cross-sectional view along the line 19-19 in FIG. 13; and

FIG. 20 is an exploded view of a portion of the cage as indicated by thecircle 20 in FIG. 14.

DETAILED DESCRIPTION

The present invention will be described with reference to theaccompanying drawing figures wherein like numbers represent likeelements throughout. Certain terminology, for example, “top”, “bottom”,“right”, “left”, “front”, “frontward”, “forward”, “back”, “rear” and“rearward”, is used in the following description for relativedescriptive clarity only and is not intended to be limiting.

Referring to FIGS. 1 and 2, a needle roller thrust bearing assembly 20that is a first embodiment of the present invention is shown. The thrustbearing assembly 20 includes a cage 22 supporting a plurality ofpreferably cylindrical rolling elements 2 arranged radially from acenter of rotation (not shown). The cage 22 comprises two cage halves24, 26. Each cage half 24, 26 includes a radially extending segment 25,27 respectively with circumferentially spaced openings 30, 32respectively. Each radially extending segment 25, 27 includes portions47, 48 circumferentially between the plurality of openings 30, 32.

The openings 30, 32 are preferably generally rectangular and configuredto receive the rolling elements 2. The cage halves 24, 26 areinterconnected with the openings 30, 32 radially and circumferentiallyaligned and with at least portions such as portions 47, 48 of theradially extending segments 25, 27 abutting one another along a plane P.The centerline of each of the rolling elements 2 lies in or in proximityto the plane P. In this embodiment, circumferential flanges 28 areprovided at the inner and outer diameters of the radial portions 25, 27to provide a piloting surface for the thrust bearing assembly 20 and toprovide additional structural rigidity for the cage 22.

Each opening 30, 32 has a flange 34 about at least a portion of or theentire opening perimeter. Each flange 34 extends outwardly from theplane P. The flanges 34 are formed in such a way as to guide and retainthe rolling elements 2. An advantage of this design over the prior artcage 3 constructions is that any portion of the cage 22 of the presentinvention that contacts the rolling elements 2 has a smooth rolled andformed surface. In contradistinction, as shown in FIG. 19, the surfacesthat contact the rolling elements 2 of the cage 3A are pierced such thatthe opening 5 is defined by rough pierced surfaces 10 which caninterfere with proper lubrication and also lead to wear.

FIG. 2 illustrates how the configuration of the thrust bearing assembly20 allows an effective lubricant film to be developed. Specifically,lubricant can be captured in the generally triangular area definedbetween the rolling element 2 and the two abutting cage halves 24, 26.The abutting portions 47 and 48 close off the triangular area betweenthe flanges 34 and prevent the lubricant from escaping circumferentiallyfrom adjacent the rolling element 2. Lubricant that either splashes intoor is carried by adhesion to the rolling element 2 into this generallytriangular area will tend to accumulate in this area and help promote ahydrodynamic lubricant film between the rolling element 2 and thesurfaces 35 of the flanges 34. The smooth, generally convex surfaces 35of the flanges 34 will minimize the “scraping” of lubricant off therolling element 2 and will help maintain the presence of lubricant inthe generally triangular area adjacent the rolling element 2. The smoothsurfaces 35 also minimize direct contact between the rolling elements 2and the cage 22, thereby reducing friction and wear.

Another form of the flange construction for rolling element openings 30,32 is shown in FIG. 3. In this case, the cage halves 24A, 26A still abuton the plane P extending along or approximately along the centerline ofthe rolling elements 2, however, the flanges 34A along the length of therolling elements 2 are divided into separate tabs 37. These tabs 37 areformed to present a smooth, generally conforming surface to the rollingelements, which is a variation of the smooth, generally convex surfaces35 shown in FIG. 2. However, the tabs 37 are directed towards theopposite side of the rolling elements 2 rather than the closest side. Inorder to secure retention of the rolling elements in both directions,the tabs 37 are arranged so as to alternate on a portion of theperimeter such as along the length of the rolling elements 2. Thissturdier construction allows a greater length of flange 34A. Thisadditional length allows for greater flexibility in the shape of theflange 34A and is particularly useful for bearing assembly 20 withrolling elements having smaller diameters and that have tighter spacerestrictions for the cage 22.

In addition to improved wear and lubrication, another advantage of thecage 22 of thrust bearing assembly 20 is the substantially greaterstrength it provides compared to existing types of cage construction.This is particularly important in those areas with high concentrationsof stress, such as the corners of the cage openings. FIG. 20 shows aportion of a prior art cage 3A, taken near the inner diameter. It can beseen that the corners 13 of the cage openings 5 must be at right anglesand relatively sharp to clear the rolling elements. The trapezoidalshape of the cage bars 14 between the openings 5 exacerbates thissituation in the prior art designs because there is minimal cagematerial to resist stresses caused by radial and torsional loads on thecage. Referring to FIG. 4, the flanges 34 of the thrust bearing assembly20 includes a continuous surface at the corners 31 of the generallyrectangular openings 30, 32. This structure can increase the cagestrength in two ways. First, the flanges 34 provide additional materialall around the openings 30 for the rolling elements 2. In the areas ofhigh stress, such as corners 31 near the inner diameter, the flanges 34can as much as double the amount of material available to resist thesestresses. The cage openings 30 are further strengthened by the actualshape of the flanges 34. The flanges 34 are designed in such a way thatthe stresses are directed away from the corners 31 of the openings 30.The combination of additional material and optimized stress flow resultsin cage strength that is several times greater than that of the priorart constructions.

There are several possible ways to interconnect the two cage halves 24,26 to form the rigid cage 22. Using the embodiment of the sealed bearingassembly 20 as shown in FIG. 3, the rolling elements 3 can be snappedpast the tabs 37 to join the cage halves 24A, 26A and form a unitarythrust bearing assembly 20.

Several additional examples of interconnecting the cage halves 24, 26are shown in FIGS. 5-8, however, other methods may also be utilized.Referring to FIG. 5, the cage halves 24, 26 are spot welded 40 atvarious points along the abutting radial portions 25 and 27. FIG. 6illustrates a mechanical joint 42 created by partially piercing theradial portions 25, 27 and locking the two halves 24, 26 together.Referring to FIG. 7, a circumferential band 44 is secured to the innerand/or outer diameters of the cage halves 24, 26 about the inner orouter flanges 28 to secure the halves 24, 26 together. In the embodimentshown in FIG. 8, one of the cage halves 26B does not have a flange, butinstead terminates in the radial portion 27. The other cage half 24B hasa flange 46 extending from the radial portion 25 that extends toward andwraps around the radial portion 27. While the flange 46 is illustratedas being along the cage outer diameter, it is also possible to providethe flange 46 along the cage inner diameter.

Another advantage of the current invention is that various combinationsof differently sized circumferential flanges 28 at the inner and outerdiameter of the cage 22 can be used to control lubricant flow within thebearing assembly 20. In some cases it is desirable to restrict orpartially restrict the lubrication flow, while in other cases it isdesirable to allow as much flow as possible. For example, FIG. 9 showsthe thrust bearing assembly 20 of FIG. 1 positioned between twostructures 50 and 52. As can be seen, the inner and outer diametercircumferential flanges 28 restrict the radial oil flow past the bearingassembly 20. FIG. 10 shows another embodiment thrust bearing assembly20C positioned between structures 50, 52. The thrust bearing assembly20C includes a cage 22C with interconnected halves 24C and 26C. Bothhalves 24C and 26C are without flanges which thereby allows more oilflow past the bearing assembly 20C. Other designs could incorporatepartial or shorter flanges 28 to partially restrict flow.

The present invention addresses the essential requirements of a thrustbearing cage, namely, structure, guidance and retention, in a mannerthan greatly improves both the strength, rigidity, lubricationadvantages, and the efficiency of the bearing assembly. Further, a lowprofile of the bearing assembly can be achieved.

Various features and advantages of the invention are set forth in thefollowing claims.

1. A thrust bearing assembly comprising: a cage having first and secondcage halves, each cage half having a respective radial segment with aninner surface, an outer surface and a plurality of circumferentiallyspaced openings, each opening having an opening perimeter, the cagehalves being interconnected such that the respective openings arealigned to define rolling element pockets; a plurality of rollingelements positioned in the rolling element pockets; and a flangeextending along at least a first portion of each opening perimeter toretain the rolling elements within a respective one of the rollingelement pockets, wherein each flange includes a generally concave outersurface and a generally convex inner surface, the generally convex innersurface of each flange being disposed in a facing relationship with anouter surface of a respective rolling element.
 2. The thrust bearingassembly of claim 1, wherein portions of the radial segmentscircumferentially between the plurality of openings abut along the innersurfaces of the first and second cage halves.
 3. The thrust bearingassembly of claim 2, wherein a centerline of each rolling element liesin a given plane defined by the abutting inner surfaces of the firstcage half and the second cage half.
 4. The thrust bearing assembly ofclaim 3, wherein at least one cage half includes an outer flange alongan outer radius, the flange extending away from the given plane.
 5. Thethrust bearing assembly of claim 3, wherein at least one cage halfincludes an inner flange along an inner radius, the flange extendingaway from the given plane.
 6. The thrust bearing assembly of claim 1,wherein the cage halves are joined together by one of spot welding, amechanical joint, a circumferentially extending clamping band, and aportion of one cage half overlapping and clamping a portion of the othercage half.
 7. The thrust bearing assembly of claim 1, wherein eachflange extends along the entire perimeter of a respective opening. 8.The thrust bearing assembly of claim 1, wherein the openings aregenerally rectangular.
 9. The thrust bearing assembly of claim 8,wherein each flange includes a continuous surface at corners of thegenerally rectangular openings.